The present invention relates generally to devices used to measure the level of a liquid within a vessel or container and more specifically to such a device which employs a plurality of serially connected thermocouple junctions arranged in laterally spaced pairs with respective thermocouple junctions of each pair being positioned in substantially parallel spaced rows.
There exists a wide variety of applications in which it is desirable to monitor to some degree the level of a liquid within a vessel or the like. Such applications may range from monitoring various fluid levels within a motor vehicle or internal combustion engine or fuel tank to monitoring oil levels within a pump or compressor or even water levels within a tank such as for a recreational vehicle or boat. In each of these applications it is desirable that the liquid level sensor be capable of providing a reliable accurate indication of the liquid level over an extended period of time without requiring periodic maintenance. In many applications the level sensor must be capable of enduring various levels of vibration, heat or other hostile environmental elements as well as space limitations. Additionally, in some applications utilizing sealed vessels such as hermetic compressors, it is desirable to minimize the number of penetrations such as electrical leads through the walls of the vessel to reduce the potential for leakage.
Various types of devices have been developed over the years for sensing such levels of liquids. Such devices range from the extremely simple float arrangement commonly employed in fuel tanks to more complex electrical capacitance type sensors as well as microprocessor based thermocouple sensors. While operable, these various types of sensors have had varying drawbacks depending upon the particular application such as excessive space requirements for accommodating movable floats and associated linkage, relatively high costs to manufacture, complexity of circuitry required to generate a level indicating signal, susceptibility to errors from extended or extraneous electrical noise, lack of resistance to hostile environmental elements, etc.
The present invention overcomes these drawbacks inherent in the prior art sensors by providing an extremely reliable sensor which is compact and simple in design and can be manufactured at very low costs. Further the present invention can be encapsulated or coated with a variety of suitable materials to enable it to maintain prolonged operation in numerous different and potentially hostile environments. The sensor of the present invention incorporates a first plurality of thermocouple junctions arranged along a substrate with a suitable heater arranged in close proximity thereto. In order to compensate for ambient temperature, a second compensating thermocouple junction is associated with each of the first thermocouple junctions and laterally spaced therefrom. The thermocouple junctions are interconnected in series with respective first and second thermocouple junctions alternating in the serial interconnection. The first ones of the thermocouple junctions provide an indication of the rate of heat dissipation which is directly related to the nature of the fluid surrounding the thermocouple junction while the second thermocouple junctions provide a compensation factor dependent upon the ambient temperature. This arrangement not only provides a very simple and reliable device for measurement of liquid levels within a container but further minimizes the number of leads that must extend through the wall of the container which may be important particularly if the liquid to be measured is part of a closed system such as for example a refrigeration system.
In another embodiment, the sensor of the present invention is a single threshold level sensor including a first thermocouple junction having a suitable heater arranged in close proximity thereto. A second compensating thermocouple junction is interconnected with the first thermocouple junction and is laterally spaced therefrom in order to compensate for ambient temperature. The first thermocouple junction provides an indication of the rate of heat dissipation which is directly related to the nature of the fluid surrounding the thermocouple junction while the second thermocouple junction provides a compensation factor dependent upon the ambient temperature. This arrangement similarly provides a simple and reliable device for measurement of liquid levels within a container while minimizing the number of leads that extend through the wall of the container.
A hermetic interface is further provided for use with the foregoing single threshold level sensor. The hermetic interface is provided to effectively seal the container generally around an area in which the sensor extends through a container wall and includes an amplifying circuit, a glass seal, and a protective shield. The hermetic seal is operable to seal the area generally around an input from the single level threshold sensor while concurrently allowing a signal from the single threshold level sensor to be received by the amplifying circuit. Specifically, the glass seal is generally bonded directly to a first series of leads extending from the amplifying circuit, thereby sealing an interior volume of the container while allowing communication through the first leads of the amplifying circuit. The first leads are selectively connected to a second series of leads extending from the single threshold level sensor for electrical communication therebetween. Finally, the protective shield axially surrounds the single threshold level sensor and serves to protect the sensor from sloshing of a fluid disposed within the container. In this manner, the hermetic interface effectively seals the container while concurrently allowing an electrical signal to be transmitted from the single threshold level sensor to the amplifying circuit.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.